Process for producing electron emitters and the product



Jan. 10, 1933. RUFFLEY 1,894,059

PROCESS FOR PRODUCING ELECTRON EMITTERS AND THE PRODUCT Filed April 8,1927 Patented Jan. 10, 1933 UNITED STATES PATENT OFFICE FREDERICKRUFFLEY, OF JERSEY CITY, NEW JERSEY, ASSIGNOR TO DE FOREST RADIOCOMPANY, OF JERSEY CITY, NEW JERSEY, A CORPORATION OF DELAWARE PROCESSFOR PRODUCING ELECTRON EMITTERS AND THE PRODUCT Application filed April8,

This invention'relat'es broadly to electron emitters. I

One of the objects of this invention is the provision of a coatingcompound for certain types of filaments to provide an efiicient electronemitter and especially one known as the Wehnelt' cathode. Y

A further object of this invention is the provision of a novel method ofpreparing the coating compound. I

A still'further object ofthis invention is the provision of a new andnovel coating compound and the method of applying it to suitable heatproducing bodies.

These and many other objects are successfully sought by means of thisinvention.

This invention resides in the combination of steps, construction,arrangement and relative location of parts as will appear more fully inthe following description.

Referring to the drawing:

Figure l is a perspective view of one form of filament employing theprinciples of my invention, and

Figure 2 is a perspective view of a modified form with some parts brokenaway.

Heretofore in the preparation of electron emitting bodies for use inaudions and similar devices it has been necessary to apply specialtreatment to the device while under construction in order to insure acomplete removal of the gases therefrom without destroying the efficacyof the emitter. I have discovered a novel coating compound which, whenapplied to filaments of the proper type, results in an alloy filamentwhich requires no special activation treatments such as electronicbombardment during the evacuation of the device in which it isto beused. The only type of treatment necessary is that of some temperatureaging after the tube has been completed. One of the special advantagesof a filament treated by the procedure of my invention is that a gettersuch as a magnesium flash may be employed to clean up the residual gasesfrom the vessel without destroying the eificiency of the filament as anelectron emitter.

The method of preparing the coating compound is as follows. A watersuspension of 1927. Serial No. 181,944.

an inert substance such as magnesia or lime 1s mixed with: barium iodideand barium acetate. I have found that a water suspen- S1011 of aconsistency of a thin paste is suitable for the purpose and one (1) gramof 5 magnesia or lime mixed with two (2) milligrams of barium iodide andone (1) gram of barium acetate will provide a suitable compound. I havefound that all organic salts of barium are desirable for this purposeas, for instance, it is possible to use barium form-ate or barium.stearatein place of the barlum acetate. WVhen this coating compound hasbeen prepared a suitable filament or heating body such as platinum or aplatinum alloy comprising platinum and nickel or iridium is heated andcoated therewith. I do not desire to be limited particularly to platinumor platinum alloy filaments since it is possible to use any metal whichwill alloy with barium for the purposes of this invention. In heatingthe filament I have found it best to heat the wire firstto a yellow heatto thoroughly clean it and then permit it to cool to a temperature wherethe body 2 5 is not visibly red and then dip the wire into the coatingcompound or otherwise apply the coating compound thereto. The heat inthe body'of thewire is sufficient to drive off the moisture and leavethe ingredients of the water suspension thereon.

This filament as prepared, is placed in any device employing cathodeelectron emitters and the vessel is exhausted by any of the usual andwell known methods without treat- .35 ing the filament by electronbombardment during the evacuation. After the vessel is sealed off thefilament is heated in the usual manner which results in a slow alloyingaction between the barium which. is easily 9'0 reducible from itscompounds with the metal of the filament as, for instance, platinum. Ihave found that the inert substance such as magnesia or lime whenemployed in the mixture results in a slowing down of this alloy actionwhich is desirable. The efliciency of a filament treated in this manneras an electron emittercontinuesover thefull life of the filament sincewhenever the filament is heated this slow alloying action is eontin- 100ually going on with the result that the barium is being freed to alloywith the filament.

I have shown in the drawing two different forms of filaments constructedin accordance with my invention. The filament body platinum, platinumalloys'or other suitable body is shown at 1 to which has been appliedthe coating compound disclosed above in any suitable manner as bydipping, spraying, brushing, etc. The coating compound has beendesignated in Figure 1 by areference numeral 2. I In Figure 2 is shown adifferent form of filament that is well known as the VVehnelt type offilament in which the heating body is shown at 3 as a thin strip ofsuitable material such as platinum to which has been applied the coatingcompound 4 prepared as described above.

I am, of course, aware that many changes in the details of procedure andrelative arrangement of steps, as well as in the ingredients andproportions thereof will readily occur to those skilled in the art, andI do not, therefore, wish to be limited to those quantities andmaterials disclosed by me for purposes of illustration, but rather tothe spirit and scope of this invention as defined in the appendedclaims. For instance, any suitable metallic filament can be used withwhich the barium will alloy; any inert substance can be used in theplace of the magnesia or lime; any of the organic salts of barium may beemployed; the particular proportions by weight of the ingredientsemployed may be varied between reasonable limits and, finally, anymethod of coating the filament may be em loyed without departing fromthe princi of my invention.

hat I seek to secure by United States Letters Patent is:

1. The method of producing treated filamente com rising mixing togethermagnesia and organic salts of barium in water and coating a suitablefilament with said mixture. 2. The method of producing treated filamentscomprising mixing together magnesia,

barium acetate and barium iodide with water to form a paste and applyingsaid paste to a.

suitable heating body.

3. The method of preparing electron emitting bodies comprising preparinga water sigpension in the form of a paste of magn a, barium iodide andbarium acetate; heating a suitable body to clean it and coating saidbody with said paste while hot.

4. The method of preparing electron emitting bodies comprising preparinga water suspension in the form of a paste of one part by weight ofmagnesia, two parts by welght of barium iodide and one part by weight ofbarium acetate and coating suitable body with said paste.

5 A filament coating mixture comprising a water suspension of magnesia,barium O6 iodide and barium acetate.

6. A filament coating mixture comprisin a water suspension of one partby weight 0 magnesium oxide, and four parts by weight of barium acetateand barium iodide.

7 An electron emitting body prepared by having a coating of magnesia,barium acetate and barium iodide.

8. An electron emitting body comprising arbase of platinum and nickelalloy and a coating of mangesia, and organic salts of barium.

9. The method of preparing electron emitting bodies comprising preparinga water suspension in the form of a paste of magnesia, barium iodide andbarium acetate; heating a body of platinum and nickel alloy find coatingsaid body with said paste while 10. A filament coating mixturecomprising barium iodide and organic salts of barium, and a material forretarding the alloying action of the barium with the filament.

In testimony whereof I have hereunto set my hand on this 29th day ofMarch A. D.,

FREDERICK RUFFLEY.

